The gesetzliche Krankenversicherung (statutory health insurance) is insurance for your health. In Germany, there are many health insurance providers you can choose from.
If you work, you pay part of your income every month. This is a fixed percentage. Your employer also pays part of the cost. If you are a student, have a Minijob, or earn very little, you often pay a fixed amount each month.
Everyone in Germany must have health insurance. The insurance pays for medical care when you are sick or need medical help.